Not applicable.
Not applicable.
Not applicable.
The present invention relates to ammonium polyphosphate fire retardants. More specifically, the present invention relates to ammonium polyphosphate fire retardants containing metal ferrites for reduced aluminum corrosion.
Aerial application of fire retardant compositions to combat the spread of wildland fires is common. The composition of fire retardant concentrates designed for managing and controlling wildland fires are of two general types, those which, when mixed or diluted with water to end-use concentration result in a gum-thickened solution, and those that do not contain a gum thickener, which are water-like solutions. The former may be supplied as dry powders or as suspensions or slurries, and are generally referred to as fluids. Those concentrates that result in water-like solutions when diluted with water may contain suspended components, as well, but are generally referred to as liquid concentrates. Fire retardant concentrates that are supplied as fluids or liquids are preferred by some because they can be diluted simply and easily to end-use strength with little mixing hardware and manpower.
Fertilizer grade ammonium polyphosphate solutions, discussed in greater detail infra, have been used as aerially applied fire retardants. These liquids have certain advantages in comparison to other fire-suppressing compositions since they can be transported and stored in the liquid form prior to use rather than being mixed from dry ingredients. However, concentrated liquid fire retardants and solutions prepared therefrom are extremely corrosive to aluminum and brass and mildly corrosive to other materials of construction used in handling, storage and application equipment. As used herein, all references to metals implicitly include reference to alloys thereof as well. Accordingly, aluminum encompasses aluminum 2024T3, 6061 and 7074, references to steel encompass 1010 and 4130 steel, and brass encompasses yellow and naval brass. Since wildland fire retardants are most frequently transported to the fire and applied aerially, it is imperative that corrosive damage to the materials of construction of fixed-wing aircraft and helicopters be minimized.
Accordingly, the United States Department of Agriculture (xe2x80x9cUSDAxe2x80x9d) Forest Service has established, in xe2x80x9cSpecification 5100-304b (January 2000) Superseding Specification 5100-00304a (February 1986),xe2x80x9d entitled xe2x80x9cSpecification for Long Term Retardant, Wildland Fire, Aircraft or Ground Applicationxe2x80x9d (hereinafter, xe2x80x9cForest Service Specificationsxe2x80x9d), hereby incorporated by reference, maximum allowable corrosion rates, and methods for calculating such corrosion rates for 2024T3 aluminum, 4130 steel, yellow brass and Az-31-B magnesium. For example, the corrosivity of forest fire retardants, in concentrate, to aluminum, steel and yellow brass must not exceed 5.0 milli-inches (xe2x80x9cmilsxe2x80x9d) per year as determined by the xe2x80x9cUniform Corrosionxe2x80x9d test set forth in Section 4.3.5.1 of the aforementioned USDA, Forest Service Specifications. If the product is applied from fixed-tank equipped helicopters, in addition to the above requirements, the corrosivity of the fire retardants to magnesium must not exceed 5.0 mils per year (xe2x80x9cmpyxe2x80x9d). The Forest Service Specifications identify the maximum amount of corrosion acceptable when both the retardant concentrate and its diluted solutions are exposed to each metal indicated above at temperatures of 70xc2x0 Fahrenheit (xe2x80x9cFxe2x80x9d) and 120xc2x0F. in both totally and partially immersed configurations. The maximum allowable corrosivity of aerially applied fire retardant diluted solutions to aluminum is 2.0 mpy, and the maximum corrosivity to brass and to steel is 5.0 mpy when totally immersed, and 2.0 mpy when tested in the partially immersed condition. In the partially immersed configuration, one-half of the coupon is within the solution and one-half is exposed to the vapors in the air space over the solution.
Sodium ferrocyanide has historically been incorporated into the corrosive compositions in an effort to address the corrosivity problems encountered with the use of fertilizer grade ammonium polyphosphates. Sodium ferrocyanide has proved to be an effective corrosion inhibitor in fire retardant compositions containing ammonium polyphosphate fertilizer solutions. However, while sodium ferrocyanide is effective as a corrosion inhibitor, several disadvantages of its use make its incorporation in wildland fire retardant compositions undesirable. Specifically, the environmental and toxicological safety of ferrocyanides as well as ferricyanides is, at best, questionable. When exposed to acidic conditions and/or ultraviolet radiation from natural sunlight, the ferro(i)cyanide radical readily degrades releasing cyanide and/or hydrogen cyanide, which are toxic to humans, animals and aquatic life. Further, free iron emanating either from decomposition of a portion of the ferrocyanide radical, or introduced from other components or impurities within the composition, will subsequently react with remaining non-decomposed ferro(i)cyanide to form ferrous ferricyanide (xe2x80x9cTumbull""s Bluexe2x80x9d) or ferric ferrocyanide (xe2x80x9cPrussian Bluexe2x80x9d), which emit a persistent blue-black or indigo-blue coloration, staining all that they contact. Consequently, neither ferricyanide nor ferrocyanide can be used in fire retardants that are expected to fade and to become non-visible over time, for example, in fugitive retardant compositions.
The magnitude of the above concerns is increased since wildland fire retardants are generally applied aerially in a less than completely controlled manner. Due to the presence of variables such as vegetative cover, smoke, or wind drift that impact the trajectory of the free-falling solution, aerially applied wildland fire retardant solutions may land on or near people, animals and in bodies of water, or on soil where it could enter the water supply.
Accordingly, there is a need to provide safe and acceptable wildland fire retardants for the suppression or management of wildland fires that are not corrosive to the equipment associated with the transportation, handling and application of the retardant, and are environmentally and toxicologically friendly, thereby avoiding the above disadvantages.
In one aspect of the invention, fire retardant compositions are provided that comprise at least one ammonium polyphosphate, at least one suspending agent and at least one metal ferrite.
In a second aspect of the invention, the above-described fire retardant compositions are provided that comprise at least one gum thickener.
In a third aspect of the invention, the above-described fire retardant compositions comprising at least one gum thickener comprise at least one gum thickener that is a biopolymer with a median particle diameter less than 100 microns.
In a fourth aspect of the invention, the above-described fire retardant compositions of the invention comprise zinc ferrite.
In a fifth aspect of the invention, the above-described fire retardant compositions of the invention comprise magnesium ferrite.
In a sixth aspect of the invention, methods of making dilute fire retardant compositions of the invention, adapted for aerial application to wildland fires, are provided that comprise forming an intermediate concentrate composition comprising the above-described composition of the invention and diluting the intermediate concentrate with water to form the dilute fire retardant composition of the invention.
In a seventh aspect of the invention, methods of retarding or suppressing wildland fires are provided that comprise the step of aerially applying a fire retardant composition comprising the diluted fire retardant compositions of the invention to wildland vegetation.